FIG. 9 shows a structure of a generally known heat-adjustable electric cooker employing a plurality of heaters.
In FIG. 9, the cooker comprises heaters 31 and 38, heat-adjuster 32 and 39 employing bimetal for adjusting heat, commercial power 33, warning lamp 34 for indicating the heater is ON, switches 35 and 40 incorporated in the heat-adjuster, bimetallic switches 36 and 41 on a control side, sub-heaters 37 and 42 for heating the bimetal and being connected to heaters 31 and 38 in series. Sub-heaters 37 and 42 are incorporated into switches 36 and 41 on the control side.
Heat of this electric cooker is adjusted in this way: bimetallic switches 36 and 41 are heated by sub-heaters 37 and 42, and the switches 36 and 41 interlock switches 35 and 40 to open or close thereof.
The conventional construction employing bimetal has the following problems: (a) a wide range of performance dispersion of bimetal in respective products are expected, (b) various types of bimetal responsive to wattage of respective heaters must be prepared in order to minimize the difference in heat value, (c) and thus fine controlling is needed, (d) a great amount of heat dissipation is wasted due to a long control duty (e) heat is applied to food with low efficiency, (f) from the view point of service life of the electric cooker, contact points must be replaced periodically due to insufficient durability, and (g) in a case of a large size appliance such as built-in type cooker in a system kitchen, a large number of heaters make the replacement cumbersome and time-consuming work, which produces serious problems in maintenance.